1. 介绍

　　使用mybatis时可以使用二级缓存提高查询速度，进而改善用户体验。

　　使用redis做mybatis的二级缓存可是内存可控<如将单独的服务器部署出来用于二级缓存>，管理方便。

2. 使用思路

　　2.1 配置redis.xml 设置redis服务连接各参数

　　2.1 在配置文件中使用 <setting> 标签，设置开启二级缓存；

　　2.2 在mapper.xml 中使用<cache type=”com.demo.RedisCacheClass” /> 将cache映射到指定的RedisCacheClass类中；

　　2.3 映射类RedisCacheClass 实现 MyBatis包中的Cache类，并重写其中各方法；

　　　　在重写各方法体中，使用redisFactory和redis服务建立连接，将缓存的数据加载到指定的redis内存中(putObject方法)或将redis服务中的数据从缓存中读取出来(getObject方法)；

　　　　在redis服务中写入和加载数据时需要借用spring-data-redis.jar中JdkSerializationRedisSerializer.class中的序列化(serialize)和反序列化方法(deserialize),此为包中封装的redis默认的序列化方法；

　　2.4 映射类中的各方法重写完成后即可实现mybatis数据二级缓存到redis服务中；

3. 代码实践

　　3.1 配置redis.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:task="http://www.springframework.org/schema/task"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
    http://www.springframework.org/schema/aop
    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
    http://www.springframework.org/schema/tx 
    http://www.springframework.org/schema/tx/spring-tx.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-3.0.xsd
    http://www.springframework.org/schema/task
    http://www.springframework.org/schema/task/spring-task-3.0.xsd" >
    <!-- enable autowire -->
    <context:annotation-config /> 
       
    <task:annotation-driven/>
    
    <context:component-scan base-package="demo.util,demo.salesorder,demo.person" />
    <!-- Configures the @Controller programming model 必须加上这个，不然请求controller时会出现no mapping url错误-->
    <mvc:annotation-driven />
    <!-- 引入数据库配置文件 -->
    <bean id="propertyConfigurer"    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>classpath:sysconfig/jdbc.properties</value>
                <value>classpath:sysconfig/redis.properties</value>
            </list>
        </property>
    </bean>
    <!-- JDBC -->
    <bean id="defaultDataSource"   class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
        p:driverClassName="${jdbc.driverClassName}"
        p:url="${jdbc.databaseurl}"
        p:username="${jdbc.username}"
        p:password="${jdbc.password}" >
        <property name="maxActive">
            <value>${jdbc.maxActive}</value>
        </property>  
        <property name="initialSize">
            <value>${jdbc.initialSize}</value>
        </property>  
        <property name="maxWait">
            <value>${jdbc.maxWait}</value>
        </property>  
        <property name="maxIdle">
            <value>${jdbc.maxIdle}</value>
        </property>
        <property name="minIdle">
            <value>${jdbc.minIdle}</value>
        </property>
        <!-- 只要下面两个参数设置成小于8小时(MySql默认)，就能避免MySql的8小时自动断开连接问题 -->
        <property name="timeBetweenEvictionRunsMillis">
            <value>18000000</value>
        </property><!-- 5小时 -->
        <property name="minEvictableIdleTimeMillis">
            <value>10800000</value>
        </property><!-- 3小时 -->
        <property name="validationQuery">
            <value>SELECT 1</value>
        </property>
        <property name="testOnBorrow">
            <value>true</value>
        </property>
    </bean>
    
    <!-- define the SqlSessionFactory -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="defaultDataSource" />
        <property name="typeAliasesPackage" value="demo.salesorder,demo.person" />
        <!-- 可以单独指定mybatis的配置文件，或者写在本文件里面。 用下面的自动扫描装配(推荐)或者单独mapper --> 
        <property name="configLocation" value="classpath:sysconfig/mybatis-config.xml" />
    </bean>
    
    
    <!-- 自动扫描并组装MyBatis的映射文件和接口-->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="demo.*.data" />
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
    </bean>
    
    <!-- JDBC END -->
    
    <!-- redis数据源 -->
    <bean id="poolConfig" class="redis.clients.jedis.JedisPoolConfig">  
        <property name="maxIdle" value="${redis.maxIdle}" />  
        <property name="maxTotal" value="${redis.maxActive}" />  
        <property name="maxWaitMillis" value="${redis.maxWait}" />  
        <property name="testOnBorrow" value="${redis.testOnBorrow}" />  
    </bean>
    
    <!-- Spring-redis连接池管理工厂 -->
    <bean id="jedisConnectionFactory" class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory">
        <property name="hostName" value="${redis.host}" />
        <property name="port" value="${redis.port}" />
        <property name="password" value="${redis.pass}" />
        <property name="timeout" value="${redis.timeout}" />
        <property name="poolConfig" ref="poolConfig" />
    </bean>      
    <!-- 使用中间类解决RedisCache.jedisConnectionFactory的静态注入，从而使MyBatis实现第三方缓存 -->
    <bean id="redisCacheTransfer" class="demo.redis.RedisCacheTransfer">
        <property name="jedisConnectionFactory" ref="jedisConnectionFactory"/>
    </bean>      
    
    <bean class="demo.util.UTF8StringBeanPostProcessor"></bean>          
</beans>    

　　3.2 mybatis.xml 配置开启二级缓存

<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE configuration 
    PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <!-- 配置mybatis的缓存，延迟加载等等一系列属性 -->
    <settings>

        <!-- 全局映射器启用缓存 *主要将此属性设置完成即可-->
        <setting name="cacheEnabled" value="true"/>

        <!-- 查询时，关闭关联对象即时加载以提高性能 -->
        <setting name="lazyLoadingEnabled" value="false"/>

        <!-- 对于未知的SQL查询，允许返回不同的结果集以达到通用的效果 -->
        <setting name="multipleResultSetsEnabled" value="true"/>

        <!-- 设置关联对象加载的形态，此处为按需加载字段(加载字段由SQL指 定)，不会加载关联表的所有字段，以提高性能 -->
        <setting name="aggressiveLazyLoading" value="true"/>

    </settings>
</configuration>

　　 3.3 在mapper.xml中映射缓存类RedisCacheClass

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="demo.person.data.UserMapper">
<cache type="demo.redis.cache.RedisCache"/> <!-- *映射语句 -->

<select id="getPersonList" parameterType="map" resultType="Person">
    select *    
     from person
    <where>
        1=1
        <if test="user_name!=null">
            and user_name=#{user_name}
        </if>    
    </where>
</select>
<insert id="addPerson" parameterType="Person" keyProperty="id" useGeneratedKeys="true">
    insert into person(
        login_id,
        user_name,
        gender,
        birthday,
        remark
    )values(
        #{login_id},
        #{user_name},
        #{gender},
        #{birthday},
        #{remark}
    )
</insert>

</mapper>

　　3.4 实现Mybatis中的Cache接口

　　　　Cache.class源码：

/*
 *    Copyright 2009-2012 the original author or authors.
 *    http://www.apache.org/licenses/LICENSE-2.0*/
package org.apache.ibatis.cache;

import java.util.concurrent.locks.ReadWriteLock;

public interface Cache {

  String getId();

  int getSize();

  void putObject(Object key, Object value);

  Object getObject(Object key);

  Object removeObject(Object key);

  void clear();

  ReadWriteLock getReadWriteLock();

}

　　　　RedisCache.java

package demo.redis.cache;

import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.ibatis.cache.Cache;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.data.redis.connection.jedis.JedisConnection;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.data.redis.serializer.JdkSerializationRedisSerializer;
import org.springframework.data.redis.serializer.RedisSerializer;

import redis.clients.jedis.exceptions.JedisConnectionException;


public class RedisCache implements Cache //实现类
{
    private static final Logger logger = LoggerFactory.getLogger(RedisCache.class);

    private static JedisConnectionFactory jedisConnectionFactory;

    private final String id;

    /**
     * The {@code ReadWriteLock}.
     */
    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public RedisCache(final String id) {
        if (id == null) {
            throw new IllegalArgumentException("Cache instances require an ID");
        }
        logger.debug("MybatisRedisCache:id=" + id);
        this.id = id;
    }

    @Override
    public void clear()
    {
        JedisConnection connection = null;
        try
        {
            connection = jedisConnectionFactory.getConnection(); //连接清除数据
            connection.flushDb();
            connection.flushAll();
        }
        catch (JedisConnectionException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (connection != null) {
                connection.close();
            }
        }
    }

    @Override
    public String getId()
    {
        return this.id;
    }

    @Override
    public Object getObject(Object key)
    {
        Object result = null;
        JedisConnection connection = null;
        try
        {
            connection = jedisConnectionFactory.getConnection();
            RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer(); //借用spring_data_redis.jar中的JdkSerializationRedisSerializer.class
            result = serializer.deserialize(connection.get(serializer.serialize(key))); //利用其反序列化方法获取值
        }
        catch (JedisConnectionException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (connection != null) {
                connection.close();
            }
        }
        return result;
    }

    @Override
    public ReadWriteLock getReadWriteLock()
    {
        return this.readWriteLock;
    }

    @Override
    public int getSize()
    {
        int result = 0;
        JedisConnection connection = null;
        try
        {
            connection = jedisConnectionFactory.getConnection();
            result = Integer.valueOf(connection.dbSize().toString());
        }
        catch (JedisConnectionException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (connection != null) {
                connection.close();
            }
        }
        return result;
    }

    @Override
    public void putObject(Object key, Object value)
    {
        JedisConnection connection = null;
        try
        {
            logger.info(">>>>>>>>>>>>>>>>>>>>>>>>putObject:"+key+"="+value);
            connection = jedisConnectionFactory.getConnection();
            RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer(); //借用spring_data_redis.jar中的JdkSerializationRedisSerializer.class
            connection.set(serializer.serialize(key), serializer.serialize(value)); //利用其序列化方法将数据写入redis服务的缓存中
            
        }
        catch (JedisConnectionException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (connection != null) {
                connection.close();
            }
        }
    }

    @Override
    public Object removeObject(Object key)
    {
        JedisConnection connection = null
        Object result = null;
        try
        {
            connection = jedisConnectionFactory.getConnection();
            RedisSerializer<Object> serializer = new JdkSerializationRedisSerializer();
            result =connection.expire(serializer.serialize(key), 0);
        }
        catch (JedisConnectionException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (connection != null) {
                connection.close();
            }
        }
        return result;
    }

    public static void setJedisConnectionFactory(JedisConnectionFactory jedisConnectionFactory) {
        RedisCache.jedisConnectionFactory = jedisConnectionFactory;
    }

}

　　4. 总结

　　　　通过重写Cache类中的方法，将mybatis中默认的缓存空间映射到redis空间中。